Lane keep assist device

ABSTRACT

A lane keep assist device is configured to perform lane keep assist control for making a host vehicle travel along a lane, and preventing the host vehicle from departing from the lane. The lane keep assist device includes an electronic control device configured to detect presence or absence of another vehicle, present in a vicinity of the host vehicle, which have a gradual decrease in a distance from the host vehicle, and when the other vehicle is detected, the electronic control device configured to set virtual line extending along front-rear direction of the detected other vehicle at position away by first predetermined distance in right-left direction of the other vehicle from lateral side of the detected other vehicle, and to specify the lane based on the set virtual line to perform the lane keep assist control.

INCORPORATION BY REFERENCE

This is a continuation of U.S. application Ser. No. 15/718,769 filedSep. 28, 2017 (allowed), which claims priority to Japanese PatentApplication No. 2016-201913 filed on Oct. 13, 2016. The entiredisclosures of the prior applications are considered part of thedisclosure of the accompanying continuation application, and are herebyincorporated by reference.

BACKGROUND 1. Technical Field

The disclosure relates to a lane keep assist device.

2. Description of Related Art

As a lane keep assist device, for example, a device is proposed in whicha determination is made whether departure from a lane by passing over alane mark is allowed based on the type of lane mark, an adjustmentoperation for correcting a course is not performed in a case where thedeparture from a lane by passing over the lane mark is allowed, and theadjustment operation for correcting a course is performed in a casewhere the departure from a lane by passing over the lane mark is notallowed. Here, particularly, when there is a risk that an object lateralto a lane along which a vehicle is traveling collides with the vehicleeven in a case where the departure from a lane by passing over the lanemark is allowed, the adjustment operation for correcting a course isperformed (see Japanese Patent No. 5350397 (JP 5350397 B)).

SUMMARY

In the technique disclosed in JP 5350397 B, it is not considered thatother vehicles traveling along lanes adjacent to a lane along which ahost vehicle is traveling thrust out to the lane along which the hostvehicle is traveling.

The disclosure provides a lane keep assist device capable of performinglane keep assist in which a relative positional relationship between ahost vehicle and other vehicles is considered.

An aspect of the disclosure relates to a lane keep assist deviceconfigured to perform lane keep assist control for making a host vehicletravel along a lane, and preventing the host vehicle from departing fromthe lane, the device including an electronic control device configuredto: detect presence or absence of other vehicle, present in a vicinityof the host vehicle, which have a gradual decrease in a distance fromthe host vehicle; and when the another vehicle is detected, set virtualline extending along front-rear direction of the detected other vehicleat position away by first predetermined distance in right-left directionof the other vehicle from lateral side of the detected other vehicle,and specify the lane based on the set virtual line to perform the lanekeep assist control.

In the lane keep assist control, the lane along which the host vehicleis traveling is specified. In a case where another vehicle is notpresent in the vicinity of the host vehicle, the lane may be specifiedby, for example, the roadside or the lane line. However, in a case whereother vehicle is present in the vicinity of the host vehicle, an area inwhich the host vehicle can travel on a road is determined by arelationship between the host vehicle and other vehicle. Specifically,for example, even in a case where the host vehicle is traveling in anarea between two lane lines on a road surface, other vehicle may comenear the host vehicle side beyond the lane line in order to avoidobstacle. In this case, when the lane along which the host vehicletravels is specified based on the lane line, there is the possibility ofthe safety of the host vehicle being threatened.

According to the lane keep assist device, when another vehicle isdetected, virtual line extending along the front-rear direction of theother vehicle is set at position away by the first predetermineddistance from the lateral side of the other vehicle, and the lane isspecified based on the set virtual line. Therefore, with the lane keepassist device, it is possible to perform lane keep assist in which arelative positional relationship between the host vehicle and othervehicle is considered.

Examples of “another vehicle having a gradual decrease in a distancefrom the host vehicle” may include an oncoming vehicle, a vehicle comingclose to the host vehicle from the rear side of the host vehicle in itstraveling direction, and a vehicle, present in front of the host vehiclein its traveling direction, which comes close to the host vehicle.

The “first predetermined distance” may be a value for setting thevirtual line, and is set as a fixed value in advance or a variable valueappropriate to some kind of physical quantity or parameters. Such a“first predetermined distance” may be set as, for example, a distanceneeded in order for the host vehicle and other vehicle to safely passeach other.

In the lane keep assist device according to the aspect, when a casewhere the other vehicle is detected, the electronic control device maybe configured to specify the lane based on the set virtual lines toperform the lane keep assist control in a case where the set virtualline is closer to the host vehicle than to a lane line on a road alongwhich the host vehicle is traveling. According to the aspect, it ispossible to perform lane keep assist in which a relative positionalrelationship between the host vehicle and other vehicle is considered,while the lane along which the host vehicle travels is prevented frombeing specified to be wider than needed.

In the lane keep assist device according to the aspect, when travelingdirection of the detected other vehicle and a traveling direction of thehost vehicle are different from each other, the electronic controldevice may configured to set the first predetermined distance to belarger than the first predetermined distance in a case where thetraveling direction of the detected other vehicle and the travelingdirection of the host vehicle are the same as each other.

In a case where the traveling directions of the host vehicle and othervehicle are different from each other, a relative velocity between thehost vehicle and the other vehicle becomes relatively high. On the otherhand, in a case where the traveling directions of the host vehicle andthe other vehicle are the same as each other, the relative velocitybetween the host vehicle and the other vehicle becomes relatively low.As described above, the first predetermined distance in a case where thetraveling directions of the host vehicle and the other vehicle aredifferent from each other may be set to be larger than the firstpredetermined distance in a case where the traveling directions of thehost vehicle and the other vehicle are the same as each other, and thusthe lane appropriate to the relative velocity between the host vehicleand the other vehicle can be specified based on the virtual line.

Meanwhile, the wording “the traveling direction of other vehicle and thetraveling direction of a host vehicle are the same as each other” is notlimited to a case where the traveling direction of the other vehicle andthe traveling direction of the host vehicle are completely the same aseach other (for example, straight lines extending along the front-reardirections of the other vehicle and a straight line extending along thefront-rear direction of the host vehicle are parallel to each other).Even in a case where the traveling directions of the other vehicle andthe traveling direction of the host vehicle deviate from each other moreor less, the wording is a concept including, in practice, a case wherethe traveling direction of the other vehicle and the traveling directionof the host vehicle are regarded as being the same as each other.

In the lane keep assist device according to the aspect, the electroniccontrol device may set the first predetermined distances to increase asa vehicle speed of the vehicle becomes higher.

In the lane keep assist device according to the aspect, in a case wherethe other vehicle is detected, the electronic control device may beconfigured to stop the lane keep assist control in a case where distancefrom a lateral side of the host vehicle to the set virtual line is lessthan a second predetermined distance in a right-left direction of thehost vehicle.

The wording “distances from a lateral side of the host vehicle to thevirtual line is less than a second predetermined distance” means that,for example, distance from the lateral side of the host vehicle to thelateral side of the other vehicle when the host vehicle and the othervehicle pass each other are excessively short. In a case where thedistance from the lateral side of the host vehicle to the virtual lineis excessively short, it is considered that a driver of the host vehiclecan recognize that the other vehicle come near (or, come close to) thehost vehicle side. In this case, safety is considered to be higher in acase where the host vehicle is controlled with the intention of a driverhimself or herself than in a case where the lane keep assist isperformed. Therefore, according to the aspect, the lane keep assistcontrol is stopped, and thus it is possible to improve safety.

The “second predetermined distance” is a value for determining whetherthe lane keep assist control is stopped, and is set as a fixed value inadvance or a variable value appropriate to some kind of physicalquantity or parameters. Such a “second predetermined distance” may beset as, for example, a distance that makes it difficult to appropriatelyperform lane keep assist in a case where the lane is specified based onthe virtual line, or a value obtained by adding a certain margin to thedistance.

In the lane keep assist device according to the aspect, the electroniccontrol device may be configured to determine whether the lane line isdrawn on a road along which the host vehicle is traveling, in a casewhere the lane line is not drawn and the other vehicle is detected, toset the virtual line extending along the front-rear direction of thedetected other vehicle at position away by the first predetermineddistance in the right-left direction of the other vehicle from thelateral side of the detected other vehicle, and to specify the lanebased on the set virtual line to perform the lane keep assist control.

In the lane keep assist device according to the aspect, the electroniccontrol device may be configured to determine whether the lane line isdrawn on a road along which the host vehicle is traveling, and tospecify the lane based on a roadside, in a case where the lane line isnot drawn and the other vehicle is not detect.

The operational effect and other advantages of an aspect of thedisclosure will become more apparent from an embodiment described below.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a block diagram illustrating a configuration of a vehicleaccording to an embodiment;

FIG. 2 is a flowchart illustrating a lane departure suppressionoperation according to the embodiment;

FIG. 3 is a flowchart illustrating a lane recognition process accordingto the embodiment;

FIG. 4 is a plan view illustrating an example of a virtual boundary lineaccording to the embodiment;

FIG. 5 is a diagram illustrating an example of a relationship between avehicle speed and a distance from the lateral side of a vehicle to bemonitored to a virtual boundary line; and

FIG. 6 is a flowchart illustrating a lane recognition process accordingto a modification example of the embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment relating to a lane keep assist device of the disclosurewill be described with reference to FIGS. 1 to 5. In the followingembodiment, a description will be given using a vehicle 1 having thelane keep assist device of the disclosure mounted therein.

Configuration of Vehicle

The configuration of the vehicle 1 will be described with reference toFIG. 1. FIG. 1 is a block diagram illustrating a configuration of avehicle according to an embodiment.

In FIG. 1, the vehicle 1 includes a brake pedal 111, a master cylinder112, a brake actuator 13, a wheel cylinder 122FL disposed at a leftfront wheel 121FL, a wheel cylinder 122FR disposed at a left rear wheel121RL, a wheel cylinder 122RL disposed at a right front wheel 121FR, awheel cylinder 122RR disposed at a right rear wheel 121RR, and brakepipes 113FL, 113RL, 113FR, 113RR.

The vehicle 1 further includes a steering wheel 141, a vibrationactuator 142, a speed sensor 151, a wheel speed sensor 152, a yaw ratesensor 153, an acceleration sensor 154, a periphery monitoring device155, a display 16, and an electronic control unit (ECU) 17 that is aspecific example of the “lane keep assist device”.

The master cylinder 112 adjusts the pressure of a brake fluid (or, anyfluid) within the master cylinder 112, in accordance with the steppedamount of the brake pedal 111. The pressure of the brake fluid withinthe master cylinder 112 is transferred to the wheel cylinders 122FL,122RL, 122FR, 122RR through the brake pipes 113FL, 113RL, 113FR, 113RR,respectively. As a result, braking forces appropriate to the pressure ofthe brake fluid transferred to the wheel cylinders 122FL, 122RL, 122FR,122RR are applied to the left front wheel 121FL, the left rear wheel121RL, the right front wheel 121FR and the right rear wheel 121RR,respectively.

The brake actuator 13 can adjust the pressure of the brake fluidtransferred to each of the wheel cylinders 122FL, 122RL, 122FR, 122RR,independently of the stepped amount of the brake pedal 111, under thecontrol of the ECU 17. Therefore, the brake actuator 13 can adjustbraking force applied to each of the left front wheel 121FL, the leftrear wheel 121RL, the right front wheel 121FR and the right rear wheel121RR, independently of the stepped amount of the brake pedal 111.

The steering wheel 141 is an operator operated by a driver in order tosteer the vehicle 1 (that is, steer a steering wheel). The vibrationactuator 142 can vibrate the steering wheel 141 under the control of theECU 17.

The ECU 17 controls the operation of the entire vehicle 1. Particularlyin the present embodiment, the ECU 17 makes the vehicle 1 travel along atraveling lane on which the vehicle is currently traveling, and performslane keep assist for suppressing the departure of the vehicle 1 from thetraveling lane. That is, the ECU 17 functions as a control device forrealizing lane keep assist including a lane keep operation (for example,lane keep assist (LKA)) and a lane departure suppression operation (forexample, lane departure alert (LDA), lane departure prevention (LDP)).

The lane keep operation means that the ECU 17 controls electric powersteering (EPS) (not shown) so that the vehicle 1 travels on, forexample, the vicinity of the center of the traveling lane, or performs acall for attention through, for example, the display 16 in a case wherethe vehicle 1 has the possibility of departing from the traveling lane.

The lane departure suppression operation means that, in a case where thevehicle 1 has the possibility of departing from the traveling lane, theECU 17 applies a yaw moment for returning the vehicle 1 to the center ofthe traveling lane to the vehicle 1 by controlling electric powersteering (so-called EPS-LDA), or applies the yaw moment to the vehicle 1by applying braking force to at least one of the left front wheel 121FL,the left rear wheel 121RL, the right front wheel 121FR and the rightrear wheel 121RR (so-called brake LDA).

Various existing aspects can be applied to the lane keep operation andthe lane departure suppression operation, and thus the description ofthe details thereof will not be given. However, an example of the lanedeparture suppression operation will be taken in order to describe theoperation of the ECU 17 that is a specific example of the “lane keepassist device”.

Lane Departure Suppression Operation

The lane departure suppression operation according to the presentembodiment will be described with reference to the flowchart of FIG. 2.The lane departure suppression operation shown in FIG. 2 is equivalentto so-called brake LDA.

In order to perform the lane departure suppression operation, the ECU 17includes a data acquisition unit 171, an LDA control unit 172, and abrake control unit 173, as processing blocks logically realized thereinor processing circuits physically realized therein.

In FIG. 2, first, the data acquisition unit 171 acquires detection dataindicating detection results of the speed sensor 151, the wheel speedsensor 152, the yaw rate sensor 153, the acceleration sensor 154 and theperiphery monitoring device 155 (step S101). The periphery monitoringdevice 155 is configured to include, for example, a camera that capturesan image of the vicinity of the vehicle 1, a millimeter-wave or infraredradar, and a light detection and ranging (LIDAR).

The LDA control unit 172 recognizes (step S2) a traveling lane on whichthe vehicle 1 is currently traveling based on the detection results orthe like of the periphery monitoring device 155 acquired in the processof step S101, and the details of traveling lane recognition will bedescribed later.

The LDA control unit 172 determines whether the traveling lane on whichthe vehicle 1 is currently traveling is a straight road or a curved roadbased on the result of the process of step S2, and calculates the radiusof curvature of the traveling lane in a case where the traveling lane isdetermined to be a curved road (step S102).

The LDA control unit 172 further calculates the current lateralposition, lateral velocity and departure angle of the vehicle 1, basedon the result of the process of step S2 (step S103). The “lateralposition” means a distance from the center of a traveling lane to thevehicle 1 (typically, distance to the center of the vehicle 1) along thedirection of lane width orthogonal to a direction in which the travelinglane extends (lane extension direction). The “lateral velocity” meansthe velocity of the vehicle 1 along the direction of lane width. The“departure angle” means an angle between the traveling lane and the axisof the vehicle 1 in its front-rear direction (for example, an anglebetween the lane line and the axis of the vehicle 1 in its front-reardirection).

The LDA control unit 172 further sets an allowable departure distance(step S104). The allowable departure distance indicates an allowablemaximum value of the departure distance of the vehicle 1 from thetraveling lane (for example, departure distance of the vehicle 1 fromthe lane line) in a case where the vehicle 1 departs from the travelinglane. Therefore, the lane departure suppression operation is anoperation for applying a yaw moment to the vehicle 1 so that thedeparture distance of the vehicle 1 from the traveling lane falls withinthe allowable departure distance.

Thereafter, the LDA control unit 172 determines whether the vehicle 1has the possibility of lane departure (departing from the traveling laneon which the vehicle is currently traveling) (step S105). Specifically,for example, the LDA control unit 172 calculates the future (forexample, after a few seconds to several tens of seconds) position of thevehicle 1, based on the current velocity, lateral position, lateralvelocity and the like of the vehicle 1. The LDA control unit 172determines whether the vehicle 1 straddles or treads the lane line atthe future position. In a case where the LDA control unit determinesthat the vehicle 1 straddles or treads the lane line at the futureposition, the LDA control unit 172 determines that the vehicle 1 has thepossibility of departing from the traveling lane.

In the determination of step S105, in a case where the LDA control unitdetermines that the vehicle 1 does not have the possibility of departingfrom the traveling lane (step S105: No), the lane departure suppressionoperation shown in FIG. 2 is terminated. Thereafter, the LDA controlunit 172 starts the lane departure suppression operation shown in FIG. 2again after a first predetermined period (for example, a fewmilliseconds to several tens of seconds) has elapsed. That is, the lanedeparture suppression operation shown in FIG. 2 is repeatedly performedwith a period appropriate to the first predetermined period.

On the other hand, in the determination of step S105, in a case wherethe LDA control unit determines that the vehicle 1 has the possibilityof departing from the traveling lane (step S105: Yes), the LDA controlunit 172 turns on a control flag relating to the brake LDA. In addition,a driver of the vehicle 1 is warned that the vehicle 1 has thepossibility of departing from the traveling lane, for example, throughthe display 16, or by applying a vibration to the steering wheel 141using the vibration actuator 142 (step S106).

In a case where the LDA control unit determines that the vehicle 1 hasthe possibility of departing from the traveling lane, the LDA controlunit 172 further calculates a new traveling locus along which thevehicle 1 traveling away from the center of the traveling lane travelstoward the center of the traveling lane. In this case, the calculatedtraveling locus satisfies the restriction of the allowable departuredistance that is set in the process of step S104.

Subsequently, the LDA control unit 172 calculates a yaw rate to begenerated in the vehicle 1 in order to make the vehicle 1 travel alongthe new traveling locus, as a target yaw rate (step S107). Next, the LDAcontrol unit 172 calculates a yaw moment to be applied to the vehicle 1in order to generate the target yaw rate in the vehicle 1, as a targetyaw moment (step S108). The LDA control unit 172 further calculatesbraking force that makes it possible to apply the target yaw moment tothe vehicle 1. In this case, the LDA control unit 172 individuallycalculates braking forces that are applied to the left front wheel121FL, the left rear wheel 121RL, the right front wheel 121FR and theright rear wheel 121RR.

Thereafter, the brake control unit 173 calculates a pressure commandvalue for specifying the pressure of a brake fluid needed for generatingthe braking force calculated by the LDA control unit 172 (step S109). Inthis case, the brake control unit 174 individually calculates pressurecommand values for specifying the pressure of the brake fluid inside thewheel cylinders 122FL, 122RL, 122FR, 122RR.

Thereafter, the brake control unit 173 controls the brake actuator 13based on the pressure command value calculated in the process of stepS109. As a result, braking force appropriate to the pressure commandvalue is applied to at least one of the left front wheel 121FL, the leftrear wheel 121RL, the right front wheel 121FR and the right rear wheel121RR (step S110).

Thereafter, the LDA control unit 172 starts the lane departuresuppression operation shown in FIG. 2 again after the firstpredetermined period has elapsed. Here, since a control flag relating tothe brake LDA is in an on-state, the lane departure suppressionoperation is started in a state where a yaw moment is applied to thevehicle 1.

In this case, in the determination of step S105 performed again, in acase where the LDA control unit determines that the vehicle 1 has thepossibility of departing from the traveling lane (step S105: Yes),processes of step S106 and the subsequent steps are performed, and thusthe application of the yaw moment to the vehicle 1 is continued. On theother hand, in the determination of step S105 performed again, in a casewhere the LDA control unit determines that the vehicle 1 does not havethe possibility of departing from the traveling lane (step S105: No),the control flag relating to the brake LDA is turned off, and theapplication of the yaw moment to the vehicle 1 is terminated (that is,the lane departure suppression operation shown in FIG. 2 is terminated).

Traveling Lane Recognition Process

Next, a traveling lane recognition process according to the presentembodiment will be described with reference to the flowchart of FIG. 3.

In FIG. 3, first, the LDA control unit 172 determines whether a laneline is drawn on the road surface of a road on which the vehicle 1 istraveling, based on the detection results of the periphery monitoringdevice 155 acquired in the process of step S101 (step S201).

In the determination of step S201, in a case where the LDA control unitdetermines that the lane line is drawn (that is, in a case where thelane line is detected) (step S201: Yes), the LDA control unit 172determines whether vehicle to be monitored are present in the vicinityof the vehicle 1, based on the detection results of the peripherymonitoring device 155 acquired in the process of step S101 (step S202).

The “vehicle to be monitored” mean a vehicle (for example, vehicle 11 inFIG. 4) coming close to the vehicle 1 from the rear side of the vehicle1 in its traveling direction, a vehicle (for example, vehicle 12 in FIG.4), present in front of the vehicle 1 in its traveling direction, towhich the vehicle 1 comes close, and an oncoming vehicle (for example,vehicle 20 in FIG. 4). Meanwhile, the “vehicle to be monitored”according to the present embodiment are an example of “another vehicle”.

In the determination of step S202, in a case where the LDA control unitdetermines that no vehicle to be monitored is present (step S202: No),the LDA control unit 172 specifies the traveling lane of the vehicle 1based on the lane line (step S206).

On the other hand, in the determination of step S202, in a case wherethe LDA control unit determines that the vehicle to be monitored ispresent (step S202: Yes), the LDA control unit 172 creates (or set) avirtual boundary line (step S203).

The virtual boundary line will be described with reference to FIG. 4.FIG. 4 is a plan view illustrating an example of a virtual boundary lineaccording to the embodiment.

In a case where the vehicle to be monitored is the vehicle 11 in FIG. 4(that is, vehicle coming close to the vehicle 1 from the rear side ofthe vehicle 1 in its traveling direction), the LDA control unit 172 setsa line bi extending along the front-rear direction of the vehicle 11, asthe virtual boundary line, at a position away by a distance Dt in theright-left direction of the vehicle 11 from the lateral side of thevehicle 11 on the vehicle 1 side.

In a case where the vehicle to be monitored is the vehicle 12 in FIG. 4(that is, vehicle, present in front of the vehicle 1 in its travelingdirection, to which the vehicle 1 comes close), the LDA control unit 172sets a line b₂ extending along the front-rear direction of the vehicle12, as the virtual boundary line, at a position away by a distance Dt inthe right-left direction of the vehicle 12 from the lateral side of thevehicle 12 on the vehicle 1 side.

In a case where the vehicle to be monitored is the vehicle 20 in FIG. 4(that is, oncoming vehicle), the LDA control unit 172 sets a line b₃extending along the front-rear direction of the vehicle 20, as thevirtual boundary line, at a position away by a distance Dc in theright-left direction of the vehicle 20 from the lateral side of thevehicle 20 on the vehicle 1 side.

As shown in FIG. 5, the distance Dt and the distance Dc monotonicallyincrease the vehicle speed of the vehicle 1 becomes higher. As shown inFIG. 5, the distance Dc is larger than the distance Dt in a case ofcomparison at the same vehicle speed. This is because a relativevelocity between the vehicle 1 and the vehicle 20 that is traveling in adirection opposite to the traveling direction of the vehicle 1 is largerthan a relative velocity between the vehicle 1 and the vehicle 11 or thevehicle 12 that is traveling in the same direction as the travelingdirection of the vehicle 1. Meanwhile, the “distance Dt and distance Dc”according to the present embodiment are an example of a “firstpredetermined distance”.

Referring back to FIG. 3, after the process of step S203, the LDAcontrol unit 172 determines whether a distance L (for example, L₁, L₂ inFIG. 4) from the lateral side of the vehicle 1 on the virtual boundaryline side to the lane line is shorter than a distance LD (for example,LDt, LDc in FIG. 4) from the lateral side of the vehicle 1 on thevirtual boundary line side to the virtual boundary line (step S204).

In the determination of step S204, in a case where the LDA control unitdetermines that the distance L is shorter than the distance LD (stepS204: Yes), the LDA control unit 172 specifies the traveling lane of thevehicle 1 based on the lane line (step S206), and performs the processesof step S102 and the subsequent steps.

On the other hand, in the determination of step S204, in a case wherethe LDA control unit determines that the distance L is not shorter thanthe distance LD (step S204: No), the LDA control unit 172 specifies thetraveling lane of the vehicle 1 based on the virtual boundary line (stepS205), and performs the processes of step S102 and the subsequent steps.

For example, in a case where the virtual boundary line is the line b₁ inFIG. 4, the distance L₁ from the lateral side of the vehicle 1 on theline b₁ side to the lane line is shorter than the distance LDt from thelateral side of the vehicle 1 on the line bi side to the line b₁, andthus the LDA control unit 172 specifies the left lane edge of thevehicle 1 in its traveling direction, based on the lane line.

On the other hand, in a case where the virtual boundary line is the lineb₃ in FIG. 4, the distance L₂ from the lateral side of the vehicle 1 onthe line b₃ side to the lane line is longer than the distance LDc fromthe lateral side of the vehicle 1 on the line b₃ side to the line b₃,and thus the LDA control unit 172 specifies the right lane edge of thevehicle 1 in its traveling direction, based on the line b₃ as thevirtual boundary line.

In the determination of step S201, in a case where the LDA control unitdetermines that the lane line is not drawn (that is, in a case where thelane line is not detected) (step S201: No), the LDA control unit 172determines whether a vehicle to be monitored is present in the vicinityof the vehicle 1, based on the detection results of the peripherymonitoring device 155 acquired in the process of step S101 (step S207).

In the determination of step S207, in a case where the LDA control unitdetermines that no vehicle to be monitored is present (step S207: No),the LDA control unit 172 specifies the traveling lane of the vehicle 1based on a roadside demarcated by, for example, a curbstone, aguardrail, a wall or a fence (step S210), and performs the processes ofstep S102 and the subsequent steps.

On the other hand, in the determination of step S207, in a case wherethe LDA control unit determines that the vehicle to be monitored ispresent (step S207: Yes), the LDA control unit 172 creates (or set) avirtual boundary line (step S208). Subsequently, the LDA control unit172 specifies the traveling lane of the vehicle 1 based on the virtualboundary line (step S209), and performs the processes of step S102 andthe subsequent steps.

Meanwhile, in a case where a plurality of vehicles to be monitored ispresent, the traveling lane recognition process shown in FIG. 3 isperformed on each of the vehicles to be monitored.

Technical Effect

In the lane keep assist including the above-described lane departuresuppression operation, the traveling lane of the vehicle 1 needs to bespecified. For example, in a case where the traveling lane of thevehicle 1 is constantly specified based on the lane line drawn on a roadsurface, and a vehicle having the possibility of coming close to thevehicle 1 beyond the lane line like, for example, the vehicle 20 in FIG.4 is present, there is the possibility of making it difficult to copewith such a case through the lane keep assist.

In the present embodiment, in a case where a vehicle to be monitored ispresent in the vicinity of the vehicle 1, the virtual boundary lineextending the front-rear direction of the vehicle to be monitored is setat a position away by the distance Dt or the distance Dc from thelateral side of the vehicle to be monitored. In a case where the laneline is drawn on a road surface, the traveling lane of the vehicle 1 isspecified based on the virtual boundary line, on a condition that thedistance from the lateral side of the vehicle 1 to the virtual boundaryline is shorter than the distance from the lateral side of the vehicle 1to the lane line. On the other hand, in a case where the lane line isnot drawn on a road surface, the traveling lane of the vehicle 1 isspecified based on the virtual boundary line.

Therefore, according to the present embodiment, even in a case where avehicle having the possibility of coming close to the vehicle 1 beyondthe lane line is present, it is possible to cope with such a casethrough the lane keep assist. That is, according to the presentembodiment, it is possible to perform lane keep assist in which arelative positional relationship between the vehicle 1 and a vehicle tobe monitored is considered. Additionally, in a case where the lane lineis drawn on a road surface, the distance from the lateral side of thevehicle 1 to the virtual boundary line and the distance from the lateralside of the vehicle 1 to the lane line are compared with each other andthen the traveling lane is specified. Therefore, it is possible toprevent the traveling lane from being specified to be wider than needs.

The “LDA control unit 172” according to the present embodiment is anexample of “detection means”. The “LDA control unit 172” and the “brakecontrol unit 173” according to the present embodiment are an example ofan “electronic control device”.

Modification Example

A modification example of the traveling lane recognition processaccording to the above-described embodiment will be described withreference to the flowchart of FIG. 6.

In the process of step S205 or S209, after the traveling lane of thevehicle 1 is specified based on the virtual boundary line, the LDAcontrol unit 172 determines whether the distance LD (for example, LDt,LDc in FIG. 4) from the lateral side of the vehicle 1 on the virtualboundary line side to the virtual boundary line is less than apredetermined value in the right-left direction of the vehicle 1 (stepS301). The “predetermined value” is an example of a “secondpredetermined distance”, and is set to, for example, 10 cm (centimeter),0 cm or the like.

The wording “the distance LD is less than a predetermined value” meansthat in a state where the vehicle 1 maintains a safe distance with avehicle to be monitored, both the vehicles have difficulty in passingeach other. Particularly, a case where the distance LD has a negativevalue refers to a case where the vehicle 1 straddles or treads thevirtual boundary line, and means that there is the possibility of thevehicle 1 colliding with or coming into contact with the vehicle to bemonitored.

In the determination of step S301, in a case where the LDA control unitdetermines that the distance LD is less than the predetermined value(step S301: Yes), the LDA control unit 172 stops the lane keep assistsuch as, for example, the lane departure suppression operation shown inFIG. 2 (step S302). This is because, in this case, safety is consideredto be higher in a case where the vehicle 1 is controlled with theintention of a driver himself or herself than in a case where the lanekeep assist is performed (that is, than in a case where the vehicle 1 isautomatically controlled).

On the other hand, in the determination of step S301, in a case wherethe LDA control unit determines that the distance LD is not less thanthe predetermined value (step S301: No), the LDA control unit 172performs the processes of step S102 and the subsequent steps (see FIG.2).

The aspect of the disclosure is not limited to the above-describedembodiment, and may be appropriately modified without departing from thescope of the disclosure that can be read from claims and the entirespecification. In addition, a lane keep assist device involving suchmodifications is also intended to be included in the technical scope ofthe disclosure.

What is claimed is:
 1. A lane keep assist device for a first vehicle,comprising: an electronic control unit programmed to: determine whethera second vehicle is present in a vicinity of the first vehicle; detectwhether a lane line is drawn on a road surface upon which the firstvehicle is traveling; based upon a determination that the second vehicleis present in the vicinity of the first vehicle, set a virtual boundaryline in a front-rear direction of the second vehicle, and at a firstpredetermined distance away from a lateral side of the second vehicle,so that the virtual boundary line passes between the first vehicle andthe second vehicle; determine whether a distance L is less than adistance LD, wherein the distance L is a distance from a lateral side ofthe first vehicle to the lane line and the distance LD is a distancefrom the lateral side of the first vehicle to the virtual boundary line;based upon L being less than LD, perform the lane keep assist controlusing the lane line of the road surface upon which the first vehicle istraveling; and based upon L not being less than LD, perform the lanekeep assist control using the virtual boundary line.
 2. The lane keepassist device according to claim 1, wherein, when a traveling directionof the second vehicle and a traveling direction of the first vehicle aredifferent from each other, the electronic control unit is furtherprogrammed to set the first predetermined distance to be larger than thefirst predetermined distance in a case where the traveling direction ofthe second vehicle and the traveling direction of the first vehicle arethe same as each other.
 3. The lane keep assist device according toclaim 1, wherein the electronic control unit sets the firstpredetermined distance to increase as a vehicle speed of the firstvehicle becomes higher.
 4. The lane keep assist device according toclaim 1, wherein when the second vehicle is detected, the electroniccontrol unit is further programmed to stop the lane keep assist controlwhen the distance LD from the lateral side of the first vehicle to thevirtual boundary line is less than a second predetermined distance in aright-left direction of the first vehicle.
 5. The lane keep assistdevice according to claim 1, wherein when the lane line is not detectedand the second vehicle is detected, perform the lane keep assist controlusing the virtual boundary line.
 6. The lane keep assist deviceaccording to claim 1, wherein when the lane line is not detected and thesecond vehicle is not detected, perform the lane keep assist controlusing a roadside of the road upon which the first vehicle is traveling.